Tire used in winter having pair of rib portions and central vertical groove with saw-tooth shape

ABSTRACT

A winter tire containing a central vertical groove which extends along a tire equator C, and rib portions  6   a  and  6   b  having sipes S are formed on the opposite sides of the central vertical groove. At a groove edge line  3 E of the central vertical groove, reference pitches P each comprises a main portion extending from an outermost origin N 1  in a tire axial direction to a terminal end N 2  closest to the tire equator, and an auxiliary portion  3   b  having a length in the tire circumferential direction smaller than that of the main portion  3   a  and passes through said origin N 1  from said terminal end N 2 , and the reference pitches P are repeated in the tire circumferential direction into a zigzag configuration. A tire circumferential direction length of the main portion is 60% or more of a tire circumferential direction length of the reference pitch P.

This application is the national phase under 35 U.S.C. § 371 of PCTInternational Application No. PCT/JP02/08233 which has an Internationalfiling date of Aug. 12, 2002, which designated the United States ofAmerica.

FIELD OF THE INVENTION

The present invention relates to a winter tire capable of enhancingdriving-in-snow performance.

BACKGROUND ART

In the case of a pneumatic tire used on a snowy road and a frozen roadin winter (“winter tire”, hereinafter), emphasis is placed on drivingperformance on an especially slippery frozen road. More specifically,there is employed a method in which the land ratio of a tread surface isincreased to increase the ground-contact area, or there is employed amethod in which the tread central portion having a long ground-contactlength in the tire circumferential direction is formed with a rib-likeland on which a sipe is disposed. In any of these methods, however, thedriving-in-snow performance, especially the driving performance in deepsnow is prone to deterioration.

The present invention has been accomplished in view of theabove-mentioned problem, and it is thus an object of the presentinvention to provide a winter tire capable of preventing a deteriorationin the driving performance on frozen roads and, in fact, capable ofenhancing the driving-in-snow performance, especially the drivingperformance in deep snow.

DISCLOSURE OF THE INVENTION

The tire of the present invention provides a winter tire containing atread surface which is provided with a central vertical groovecontinuously extending along the tire equator in the tirecircumferential direction, the central vertical groove being formed atits opposite sides with rib portions having sipes, said rib portionscontinuously extending substantially in the tire circumferentialdirection.

The opposite side groove edge lines, where the groove wall surfaces onopposite sides of the central vertical groove intersect with the treadsurface includes an inclining component which inclines with respect tothe tire circumferential direction.

The groove wall surfaces contain reference pitches comprising

-   -   main portions extending from an origin which is at the outermost        side in the tire axial direction to a terminal end which is        closest to the tire equator, and    -   auxiliary portions having a length in the tire circumferential        direction which is shorter than that of the main portion and        extending from the terminal end on a line in the tire        circumferential direction passing through the origin the main        and auxiliary portions are repeatedly formed along the central        groove.

the length of the main portion in the tire circumferential direction is60% or higher than a length of the reference pitch in the tirecircumferential direction.

The auxiliary portion comprises only an axial direction component whichextends in the tire axial direction so that the groove edge line has asaw-tooth shape.

In the opposite side the groove edge lines, the tire circumferentialdirection lengths of the reference pitches are the same, and the mainportions are inclined in the same direction, phase of the referencepitch is deviated in position in the tire circumferential direction,

groove width wide portions formed between auxiliary portions which areopposed to each other in the tire circumferential direction on theopposite sides of the tire equator, and

groove width narrow portions formed between the main portions on theopposite sides of the tire equator are alternately repeated in the tirecircumferential direction,

a minimum groove width of the groove width narrow portion is 2 to 7% ofa nominal width of the tire.

In the opposite side the groove edge lines, the tire circumferentialdirection lengths of the reference pitches are the same, and the mainportions are inclined in the same direction, phase of the referencepitch is deviated in position in the tire circumferential direction,

groove width wide portions formed between auxiliary portions which areopposed to each other in the tire circumferential direction on theopposite sides of the tire equator, and

groove width narrow portions formed between the main portions on theopposite sides of the tire equator are alternately repeated in the tirecircumferential direction,

a maximum groove width of the groove width wide portion is 1.5 to 2.5times of a minimum groove width of the groove width narrow portion.

A length of the groove width wide portion in the tire circumferentialdirection is 0.2 to 0.7 times of a length of the reference pitch in thetire circumferential direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a development view of a tread pattern of a winter tire showingan embodiment of the present invention.

FIGS. 2(A) and (B) are partially enlarged views showing otherembodiments of a rib portion.

FIGS. 3(A) and (B) are sectional views for explaining a groove edgeline.

FIG. 4 is a development view of a tread pattern of the winter tireshowing another embodiment of the invention.

FIG. 5 is a development view of the tread pattern of the winter tireshowing further another embodiment of the invention.

FIG. 6 is a development view of the tread pattern of the winter tireshowing further another embodiment of the invention.

FIG. 7 is a development view of the tread pattern of the winter tireshowing further another embodiment of the invention.

FIG. 8 is a development view of the tread pattern of the winter tireshowing further another embodiment of the invention.

FIG. 9 is a development view of the tread patterns of tires ofcomparative examples 1 and 2.

FIG. 10 is a development view of the tread pattern of a tire of acomparative example 3.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be explained below based onthe drawings.

FIG. 1 is a view of a tread surface of a winter tire (simply “tire”hereinafter) of this embodiment. The tread surface 2 is formed with acentral vertical groove 3 which continuously extends on the tire equatorC in the tire circumferential direction. Inner vertical grooves 4 andouter vertical grooves 5 are formed on opposite outer sides of thecentral vertical groove 3.

In this example, rib portions 6 a and 6 b which have sipes S . . . andwhich continuously extend substantially in the tire circumferentialdirection are formed between the central vertical groove 3 and the innervertical grooves 4, respectively. The expression that the rib portions 6a and 6 b are continuous substantially in the tire circumferentialdirection includes the case as shown in FIG. 2 a, in which the land iscompletely divided by a thin groove G1 having a groove width of 3 mm orless which does not substantially hinder the continuity of the land, andthe case as shown in FIG. 2 b in which the thin groove G2 is terminatedbefore it divides the land.

Such rib portions 6 a and 6 b can secure the ground-contact area in awide range in the tire circumferential direction in the central portionof a tread surface where the ground-contact length is increased. This isof use in enhancing the driving performance on a frozen road. The widthof each of the rib portions 6 a and 6 b in the tire axial direction is0.05 to 0.2 times of a nominal width of the tire for example, and morepreferably about 0.07 to 0.16 times. The width of each of the ribportions 6 a and 6 b is varied in the tire circumferential direction insome cases, and in such a case, its average width is employed. Here,“nominal width of tire” means 195 mm when a tire size is declared as“195/65R15”. Block lines 7 and 9 comprising blocks b which are dividedby lateral grooves 10 are formed on outer sides of the rib portions 6 aand 6 b, and they are not especially limited to this embodiment.

In the tire 1 of this embodiment, in order to enhance the drivingperformance on both the frozen road and snow road, a land ratio is setto 0.65 or higher, more preferably about 0.65 to 0.75. The land ratio isa ratio of a total area of a land portion (block, rib portion) to atotal area of ground-contact region (tread ground-contact width×tireaverage circumferential length). If the land ratio is less than 0.65,the groove area is increased and this is advantageous for the drivingperformance on a snow road, but the friction force on the frozen roadbecomes small, and the driving performance is prone to deterioration. Ifthe land ratio exceeds 0.75 on the other hand, the land area isincreased. This is advantageous for driving performance on a frozenroad, but driving performance on a snowy road is prone to deterioration.

In this example, the sipe S includes components in the tire axialdirection. Sipes having a bent portion which is bent in a corrugated orzigzag shape is preferable because the edge effect can be enhanced andthe driving performance on a frozen road can be enhanced. In thisexample, not only the rib portions 6 a and 6 b, but also the block b areformed with the sipes S. The pitch of the sipes S in the tirecircumferential direction is not especially limited, but, for example,about 3.5 to 7.0 mm is preferable. It is preferable that sipe pitches L1of the rib portions 6 a and 6 b in which ground-contact pressure isincreased is set to a value smaller than the sipe pitch L2 of the blockb, more preferably, a ratio (L2/L1) is set to 1.1 to 1.2, and whenrigidities of the rib portions 6 a and 6 b are lowered, balance withrespect to rigidity of the block b in the circumferential direction isenhanced, and this is advantageous for deviated wear.

As can be seen from FIGS. 1 and 4–8, the sipes S are not opened at aposition of the origin.

As shown in FIGS. 1 and 3( a), the groove edge line 3E, where groovewall surfaces Ga and Ga on opposite sides of the central vertical groove3 intersect with the tread surface 2 a, includes inclining componentswhich incline with respect to the tire circumferential direction;reference pitches P including main portions 3 a extending from an originN1 which is at the outermost side in the tire axial direction to aterminal end N2 which is closest to the tire equator C; and auxiliaryportions 3 b having a length in the tire circumferential direction whichis shorter than that of the main portion 3 a and extends from theterminal end N2 on a line F in the tire circumferential directionpassing through the origin N1, are repeatedly formed the length La ofthe main portion 3 a in the tire circumferential direction is 60% orhigher than the length Pa of the reference pitch P in the tirecircumferential direction. As shown in FIG. 3( b), when the treadsurface 2 a and the groove wall surface Ga intersect with each otherthrough an arc portion R, the groove edge line 3E is specified at anintermediate position of the arc.

Generally, behavior of the rib portions 6 a and 6 b in which theground-contact pressure of the tread surface 2 is high andground-contact length becomes great is very pertinent to an initialresponse when the steering wheel of a vehicle is turned (slip angle isapplied to a tire). On a dry asphalt road surface having a relativelyhigh coefficient of friction μ, the rib portions 6 a and 6 b are twistedbetween themselves and the road surface by the slip angle, and thelateral force for restoring the twist by resiliency is generated, andthe initial response is enhanced.

On the other hand, on a road surface such as snow road or frozen roadhaving a low coefficient of friction μ, since the frictional forcebetween the road surface and the rib portions 6 a and 6 b is small, ifthe rigidity of the rib portions 6 a and 6 b is great, when the slipangle is applied, slip is caused before the rib portions 6 a and 6 b aresufficiently twisted and deformed, and the initial responsedeteriorates. Thus, in the present invention, the reference pitch P ofthe central vertical groove 3 is constructed as described above, and therib portions 6 a and 6 b are provided with sipes S, and based on theabove-mentioned structure, the rigidity of the rib portions 6 a and 6 bis lowered appropriately in accordance with an icy road, and the initialresponse at the time of operation of the steering wheel on a snowy roador a frozen road can be enhanced.

The main portion 3 a comprises only the inclining component which, inthis example, inclines with respect to the tire circumferentialdirection. The origin N1 of the main portion is located at the outermostside in the tire axial direction, and the terminal end N2 is locatedclosest to the tire equator. The shape of the main portion 3 a is notlimited in the case where the main portion 3 a includes an incliningcomponent which inclines with respect to the tire circumferentialdirection, and includes the origin N1 and terminal end N2. When the mainportion 3 a is straight as in this example, an inclining angle α withrespect to the tire circumferential direction is not especially limited,but it is preferable that the angle is set to about 5 to 20°, morepreferably 10 to 15°. When the main portion 3 a is not straight, it ispreferable that a straight line connecting the origin N1 and theterminal end N2 is set to the above-mentioned angle α. If the angle α ofthe main portion 3 a is less than 5°, the rigidity of the rib portions 6a and 6 b is prone to be large, and the initial response at the time ofturning on an icy road is prone to deterioration. If the angle exceeds20° on the contrary, the rigidity of the rib portions 6 a and 6 b isprone to be excessively small, and there is the adverse possibility thatdeviated friction is generated or the steering stability isdeteriorated.

The auxiliary portion 3 b has a length in the tire circumferentialdirection smaller than that of the main portion 3 a, and extends on theline F in the tire circumferential direction from the terminal end N2passing through the origin N1. The auxiliary portion 3 b in this examplecomprises only the axial direction component extending along the tireaxial direction. Therefore, the auxiliary portion 3 b does notsubstantially have a component in the tire circumferential direction.The auxiliary portion 3 b may be constituted by various straight lines,curves or combinations thereof, only if the auxiliary portion 3 bextends on the line F in the tire circumferential direction from theterminal end N2 passing through the origin N1. The length of theauxiliary portion 3 b in the tire axial direction is substantially equalto a length of the axial direction component of the main portion 3 a.With this design, the groove edge line 3E in this embodiment is formedinto a so-called sawtooth-like shape when the entire groove edge line 3Eis viewed, and this can optimize the rigidity of the rib portions 6 aand 6 b. It is of course possible that the outer edges of the ribportions 6 a and 6 b in the tire axial direction can be constituted bynot only the illustrated straight lines, but also various shapes.

In the present invention, a tire circumferential direction length La ofthe main portion 3 a is limited to 60% or higher of a tirecircumferential direction length Pa of the reference pitch P, but morepreferably 80% or higher, and more preferably 100%, and in thisembodiment, the tire circumferential direction length La issubstantially 100%. If the tire circumferential direction length La ofthe main portion 3 a is less than 60% of the tire circumferentialdirection length Pa of the reference pitch P, the rigidity variation ofthe rib portions 6 a and 6 b on a road surface having a low coefficientof friction is increased, the torsion deformation is deteriorated, andadhesion of the tread surface with respect to a road surface isdeteriorated.

In this embodiment, in the groove edge lines 3E and 3E on the right andleft sides of the central vertical groove 3, the tire circumferentialdirection lengths Pa of the reference pitch P are the same, and the mainportions 3 a are inclined in the same direction, i.e., the tirecircumferential direction, and the phase of the reference pitch Pdeviates in position in the tire circumferential direction. With thisdesign, in the central vertical groove 3, groove width wide portions 12formed between auxiliary portions 3 b and 3 b which are opposed to eachother in the tire circumferential direction on the opposite sides of thetire equator C, and groove width narrow portions 13 formed between themain portions 3 a and 3 a on the opposite sides of the tire equator Care alternately repeated in the tire circumferential direction.

When running on a snow road, such a central vertical groove 3 can form alarge snow column by pushing and treading snow in the groove width wideportion 12, and the vehicle can run while shearing the snow column bythe auxiliary portion 3 b. At that time, the greater the snow column is,the greater the shear force becomes. Therefore, according to the tire ofthe present embodiment, the driving force and braking force on a snowyroad can be increased. If the tire circumferential direction length Laof the main portion 3 a is less than 60% of the tire circumferentialdirection length of the reference pitch P, there is a tendency that thedifference of snow columns formed by the groove width wide portion 12and narrow portion 13 becomes small, and great snow column shear effectcan not be obtained.

A minimum groove width W2 of the groove width narrow portion 13 is notespecially limited, but it is preferable that the minimum groove widthW2 is 2 to 7% of the nominal width of the tire, and more preferably 3 to5%. If the minimum groove width W2 of the groove width narrow portion 13is less then 2% of the nominal width of the tire, it is difficult toform the snow column for enhancing the driving performance in the groovewidth narrow portion 13, and there is a tendency that this does notcontribute to the enhancement of the driving force. If the minimumgroove width W2 of the groove width narrow portion 13 exceeds 7% of thenominal width of the tire, there is an inconvenience that since the landratio becomes small, the driving performance on a frozen road is proneto deterioration. In the central vertical groove 3, since the groovewidth of the groove width narrow portion 13 is small, it is verydifficult to form the snow column, but by limiting the groove width ofthis portion, it is possible to enhance the driving force on a snowyroad more effectively.

Further, maximum groove width W1 of the groove width wide portion 12 isnot especially limited either, but in order to form a large snow columnand to obtain the driving force on the snow road effectively, it ispreferable that the maximum groove width W1 is 1.5 to 2.5 times of theminimum groove width W2 of the groove width narrow portion 13, and morepreferably 1.8 to 2.2 times. A length K of the groove width wide portion12 in the tire circumferential direction is equal to a deviation amountin phase of the reference pitch P in the opposite side groove edge lines3E and 3E. From the above-mentioned view point, it is preferable thatthe length K is 20 to 70% of the tire circumferential direction lengthLa of the reference pitch P, more preferably 20 to 40%. A groove depthof the central vertical groove 3 is not especially limited, but it ispreferable that the depth is about 8 to 12 mm, more preferably about 9to 11 mm.

It is preferable that the tire circumferential direction length La ofthe reference pitch P is set such that 50 or more groove width wideportions 12 are formed on one round of the tire 1, or three or morereference pitches P exist in each groove edge line 3E in theground-contact surface of the tire.

FIG. 4 shows another embodiment of the invention.

In this example, the main portion 3 a comprises an inclining component 3a 1, which is extended straight with respect to the tire circumferentialdirection from the origin N1 and is inclined, and a circumferentialdirection component 3 a 2 which is extended from the other end of theinclining component 3 a 1 to the terminal end N2 along the tirecircumferential direction. When a portion of the groove edge line 3Ewhich is closest to the tire equator is continuously in the tirecircumferential direction, the terminal end N2 is a point which isfurthest from the origin N1. In this manner, the main portion 3 a cancomprise two or more components having different angles with respect tothe tire circumferential direction.

FIG. 5 shows further another embodiment of the present invention. Inthis example, the reference pitch P comprises an inclining component inwhich the auxiliary portion 3 b is directed in the opposite directionfrom the main portion 3 a and inclined with respect to any of the tireaxial direction and the tire circumferential direction.

FIG. 6 shows a further embodiment of the present invention. In thisexample, the main portion 3 a and the auxiliary portion 3 b are arccurves in the groove edge line 3E.

FIGS. 7 and 8 show still further embodiments of the present invention.In FIG. 7, inclinations of the main portions 3 a of the left and rightgroove edge lines 3E ane 3E are in opposite directions. In FIG. 8, thetire circumferential direction lengths of the reference pitches P in theleft and right groove edge lines 3E and 3E have a differentconfiguration.

EMBODIMENT

Winter tires having a tire size of 195/65R14 were prototyped inaccordance with the specifications (structures are common exceptpattern) shown in Table 1, and the tires were mounted to all wheels of aJapanese FR passenger car having a piston displacement of 2000 cc, and arunning test was carried out on a snow circuit test course. The testscarried out included starting, state of acceleration, braking state,response at the time of cornering, and running performance through theentire distance in deep snow using 10 point scoring by a driver'ssensory evaluation. The tire rim used was 6·½ JJ and the internal tirepressure was 200 kPa.

Tires of the embodiments 1 to 3, respectively, employed the patternsshown in FIGS. 1, 4 and 5. Tires of comparative examples 1 to 3,respectively, employed the patterns shown in FIGS. 9 and 10. The resultsof the test are shown in Table. 1.

TABLE 1 (Tire size 195/65R15) Comparative Comparative ComparativeEmbodiment Embodiment Embodiment example 1 example 2 example 3 1 2 3Figure showing pattern FIG. 9 FIG. 9 FIG. 10 FIG. 1 FIG. 4 FIG. 5 Anglewith respect to tire — — 20 15 18.0 18 circumferential direction of mainportion [°] Length of main portion in tire — — 33 33 33 28circumferential direction [mm] Angle with respect to tire — — −20 90 9050 circumferential direction of auxiliary portion [°] Length ofauxiliary portion in tire — — 33 0 0 5 circumferential direction [mm]Ratio (La/Pa) [%] — — 50 100 85 85 Groove width W2 of narrow groovewidth 15 22 18 12 10 12 portion [mm] Groove width W1 of wide groovewidth 15 22 18 20 20 22 portion [mm] Length of wide groove width portionin 0 0 0 12 12 17 tire circumferential direction [mm] Ratio (K/Pa) [%] 00 0 36 36 52 Results Start, acceleration 6 6 6 7 7 7 of test performanceBraking performance 6 6 6 7 7 7 Response at the time of 6 6 7 7 7 7cornering Running performance 6 7 6 7 7 7 through whole distance in deepsnow

As a result of the test, it could be confirmed that the tires of theembodiments 1 to 3 are more excellent than tires of the comparativeexamples. Next, based on the tire of the embodiment 1, tires whoseminimum groove widths of the groove width narrow portions were variouslychanged were prototyped, and the same test was carried out. The resultsof the test are shown in Table 2.

TABLE 2 (Tire size 195/65R15) Embodiment Embodiment EmbodimentEmbodiment Embodiment Embodiment 1 4 5 6 7 8 Ratio (groove width (mm) of3.0 3.5 4.0 4.5 5.0 5.5 narrow width portion)/nominal width (mm) oftire) [%] Results Start, acceleration 7 7 7 7 7 7 of test performanceBraking performance 7 7 7 7 7 7 Response at the time 7 7 7 7 7 7 ofcornering Running performance 6 6 7 7 8 8 through whole distance in deepsnow

As explained above, according to the pneumatic tire of the presentinvention, rib portions having sipes and continuously extendingsubstantially in a tire circumferential direction are formed on oppositesides of a central vertical groove which continuously extends along thetire equator in the tire circumferential direction. Such a rib portioncan form a contact portion which is long in the tire circumferentialdirection in a tread surface central portion having high ground-contactpressure, and good driving performance on a frozen road can bemaintained. Further, by limiting the shape of the groove edge line ofthe central vertical groove, it is possible to appropriately lower therigidity of the rib portion on an icy road, and even when the slip angleis given, the following ability with respect to torsion deformationbetween the tire and the road surface is enhanced, and thus it ispossible to prevent early slip.

Further, when the auxiliary portion comprises only an axial directioncomponent extending in the tire axial direction, the groove edge linehas a sawtooth-like shape, and the above effect can further be enhanced.

In addition, the central vertical groove can contain groove width wideportions and groove width narrow portions which are alternately providedin the tire circumferential direction. Therefore, it is possible to pushand tread the snow in the groove width wide portion to form a large snowcolumn when running on a snowy road, and the vehicle advances whileshearing the column by the groove width narrow portion or the like andas a result, it is possible to increase the driving force on the snowyroad.

INDUSTRIAL APPLICABILITY

As described above, the tire of the present invention is capable ofpreventing the deterioration of the driving performance on a frozenroad, and, in fact is capable of enhancing the driving-in-snowperformance, especially the driving performance in deep snow, and thusthe tire can be advantageously used as a winter tire on an icy road.

1. A winter tire containing a tread surface which is provided with apair of rib portions having sipes and continuously extending in the tirecircumferential direction, said rib portions being provided with grooveswhich do not completely divide the rib portions, said grooves having awidth of 3 mm or less, and a central vertical groove disposed betweensaid pair of rib portions and continuously extending on a tire equatorin a tire circumferential direction, wherein side groove edge linesdefined as lines in which groove wall surfaces on opposite sides of saidcentral vertical groove intersect with a tread surface, are composed ofreference pitches repeated in the tire circumferential direction, eachof said reference pitches comprises a main portion including at least aninclining component which inclines with respect to the tirecircumferential direction, and extending from an origin being at anoutermost side in the tire axial direction to a terminal end beingclosest to the tire equator, and an auxiliary portion consisting of anaxial direction component which extends in parallel with the tire axialdirection from said terminal end to a line in the tire circumferentialdirection passing through said origin so that said groove edge line hasa saw-tooth shape, and a length (Pa) of said reference pitch in the tirecircumferential direction is larger than a pitch (L1) between said sipesin the tire circumferential direction.
 2. The winter tire according toclaim 1, wherein in the opposite side of said groove edge lines, thelength (Pa) of the reference pitches are the same, and said mainportions are inclined in the same direction, the phase of said referencepitch is being deviated in position in the tire circumferentialdirection, groove width wide portions are formed between said auxiliaryportions which are opposed to each other in the tire circumferentialdirection on the opposite sides of the tire equator, and groove widthnarrow portions which are formed between said main portions on theopposite sides of the tire equator are alternately repeated in the tirecircumferential direction, and a minimum groove width (W2) of saidgroove width narrow portion in the tire axial direction is 2 to 7% of anominal width of the tire.
 3. The winter tire according to claim 2,wherein a length (K) of said groove width wide portion in the tirecircumferential direction is 0.2 to 0.7 times the length (Pa) of saidreference pitch in the tire circumferential direction.
 4. The wintertire according to claim 2, wherein in the opposite side of said grooveedge lines, the length (Pa) of the reference pitches are the same, andsaid main portions are inclined in the same direction, the phase of saidreference pitch is being deviated in position in the tirecircumferential direction, groove width wide portions which are formedbetween said auxiliary portions which are opposed to each other in thetire circumferential direction on the opposite sides of the tireequator, and groove width narrow portions formed between said mainportions on the opposite sides of the tire equator being alternatelyrepeated in the tire circumferential direction, a maximum groove width(W1) of said groove width wide portion in the tire axial direction is1.5 to 2.5 times of a minimum groove width (W2) of said groove widthnarrow portion in the tire axial direction.
 5. The winter tire accordingto claim 1, wherein in the opposite side of said groove edge lines,length (Pa) of the reference pitches are the same, and said mainportions are inclined in the same direction, the phase of said referencepitch being deviated in position in the tire circumferential direction,groove width wide portions are formed between said auxiliary portionswhich are opposed to each other in the tire circumferential direction onthe opposite sides of the tire equator, and groove width narrow portionswhich are formed between said main portions on the opposite sides of thetire equator are alternately repeated in the tire circumferentialdirection, and a maximum groove width (W1) of said groove width wideportion in the tire axial direction is 1.5 to 2.5 times of a minimumgroove width (W2) of said groove width narrow portion in the tire axialdirection.
 6. The winter tire according to claim 5, wherein a length ofsaid groove width wide portion in the tire circumferential direction is0.2 to 0.7 times the length (Pa) of said reference pitch in the tirecircumferential direction.
 7. The winter tire according to claim 1,wherein the sipes or the grooves having a width of 3 mm or less are notopened at a position of said origin.
 8. The winter tire according toclaim 1, wherein an outer side edge line of said rib portion in the tireaxial direction is a straight line extending in the tire circumferentialdirection.
 9. The winter tire according to claim 1, wherein at least onerow of blocks having sipes and arranged in the tire circumferentialdirection is further provided axially outside of said rib portion, and aratio (L2/L1) of a pitch (L2) between the sipes of said blocks in thetire circumferential direction and said pitch (L1) between the sipes ofsaid rib portion is from 1.1 to 1.2.
 10. The winter tire according toclaim 1, wherein said main portion comprises said inclining componentwhich inclines with respect to the tire circumferential direction andwhich extends straightly from said origin, and a circumferentialdirection component which extends substantially straight from saidinclining component to said terminal end in the tire circumferentialdirection.
 11. The winter tire according to claim 1, wherein theinclining component of the main portion is curved.
 12. The winter tireaccording to claim 1, wherein the main portions on the opposite sides ofthe tire equator are inclined in the opposite direction to each other.13. The winter tire according to claim 1, wherein the length (Pa) of thereference pitches on the opposite sides of the tire equator aredifferent to each other.
 14. The winter tire according to claim 1,wherein in the opposite side of said groove edge lines, the length (Pa)of the reference pitches are the same, and said main portions areinclined in the same direction, the phase of said reference pitch beingdeviated in position in the tire circumferential direction, groove widthwide portions are formed between the auxiliary portions which areopposed to each other in the tire circumferential direction on theopposite sides of the tire equator, groove width narrow portions whichare formed between said main portions on the opposite sides of the tireequator are alternately repeated in the tire circumferential direction,and said groove width wide portions has a shape of a parallelogramincluding a pair of sides parallel with the tire axial direction so asto provide a groove width in the tire axial direction which issubstantially constant.